1. Fields of the Invention
The present invention relates to a radiotracer precursor, especially to a radiotracer precursor containing an organic ligand, 6-(2-nitroimidazde)-hexyl-L-3,6-diaza-4,7-dioxo-8 [(triphenylmethyl)thio]-2-[((triphenylmethyl)thio)methyl]octanamide (DANI), a radiotracer and a method for preparing the same.
2. Descriptions of Related Art
A lot of diseases cause hypoxia. Tissues or organs are deprived of adequate oxygen supply. For example, people have serious diseases such as stroke, myocardial infarction, malignant tumor, etc., their tissues have decreased oxygen supplies (hypoxia). This is due to acute or temporarily reduction of regional blood flow at myocardial cells or insufficient oxygen supply to malignant cells. Hypoxia is unpredictable. Thus non-invasive techniques for detecting hypoxia at various regions such as heart, brain, and tumor have been developed vigorously.
All mammals require oxygen for tissue metabolism. Generally, oxygen with low concentration (about 3˜5 torr) flows from capillaries to cells therearound for metabolism/reactions in cells. Yet tumor causes changes in oxygen balance inside tissues. In order to maintain cell activity, tumor cells need additional oxygen supply. In order to meet such requirement, tumors cells have a specific feature that is to induce blood vessel growth in tissues. However, the amount of oxygen the malignant cells need is always larger than that of the oxygen the blood vessels supply. When oxygen gas diffuses across the cell membrane of capillaries, it is quickly metabolized by cells on outer layers and unable to diffuse into inner layers of the tumor. Thus cells inside solid tumors with larger size are in hypoxia due to insufficient oxygen and blood supply and cell breakdown (necrosis) occurs gradually after long term oxygen depletion. Therefore tumors include a certain ratio of hypoxic or necrosis cells in accordance with volume and biological characters of tumors.
For diagnosis and follow-up of the malignant tumors, hypoxic tissues are of great potential to be used as media/targets being detected by radionuclide imaging techniques.
Nuclear medicine imaging involves applications of radioisotopes in medical imaging for patients. Radiopharmaceuticals are taken internally, for example, intravenously, orally or inhaledly.
After a period of time, the radiopharmaceuticals are attracted to specific organs or tissues. Then medical imaging machines such as gamma cameras are used to detect distribution of the radiopharmaceuticals in organs or tissues. For example, crystal of sodium iodide in the camera scintillates in response to incident gamma radiation so as to form images After development or computer processing, the images showing physiological changes are used as a diagnostic tool by doctors.
For detecting tumors hypoxia in vivo by radionuclide imaging techniques, a suitable radiotracer is a key factor.